1. Field of the Invention
The present invention relates to an electro-developing type video camera using an electro-developing recording medium in which an optical image obtained through a photographing lens system is electronically and directly recorded and developed as a visible image in very little time, and more particularly to relates to such an electro-developing type video camera constituted such that a developed image of the electro-developing recording medium can be optically and electronically read.
2. Description of the Related Art
Such an electro-developing recording medium per se is known. For example, Japanese Unexamined Patent Publication No. 5-2280 and U.S. Pat. No. 5,424,156 disclose one type of electro-developing recording medium comprising an electrostatic information recording medium and an electric charge keeping medium. The electrostatic information recording medium includes a photoconducting layer and an inorganic oxide material layer, and the electric charge keeping medium includes a liquid crystal display, both mediums being combined to face each other with a small gap therebetween.
An electronic still video camera using the electro-developing recording medium has already been proposed, and is referred to as an electro-developing type camera hereinafter.
In a photographing operation of the electro-developing type camera, a voltage is applied to the electro-developing recording medium, and an optical image is formed on a light receiving surface of the electrostatic information recording medium by a photographing optical system. An electric charge is distributed over the electrostatic information recording medium in accordance with a light intensity distribution of the optical image formed on the light receiving surface thereof, so that the intensity of an electric field, acting on the liquid crystal of the electric charge keeping medium, is in accordance with the electric charge distribution.
Thus, the optical image is reproduced in the electric charge keeping medium as a visible image. Namely, as soon as the optical image is formed on the electrostatic information recording medium, the optical image is recorded and developed in the electric charge keeping medium.
When the electric charge keeping medium is constituted as a memory-type liquid crystal display using, for example, a smectic liquid crystal, the developed visible image can be kept therein even if the electric field is eliminated from the electro-developing recording medium. In this case, the electro-developing recording medium carrying the developed visible image can be preserved in the same way as slides or transparency sheet films.
Also, in the memory type liquid crystal display, the developed image can be erased by heating the display to a given temperature. In this case, the same electro-developing recording medium can be repeatedly used for photographing.
Under these circumstances, the electro-developing recording medium carrying the developed visible image may be mistaken for a blank recording medium, and erroneously loaded into a camera. If the loaded medium is subjected to a second exposure, the first developed visible image is lost from the medium, and the newly-photographed image cannot be properly recorded and developed thereon.
Further, a developed recording medium is not usually unloaded from the camera immediately after photographing. Thus, the developed recording medium is frequently subjected to a double exposure, resulting in the problem mentioned above.